Apple's Mac sales are up more than 20 percent this quarter compared to the same quarter last year, and the company will get a further bump when it refreshes its MacBook line, an analyst said today.

Apple's Mac sales are up more than 20% this quarter compared to the same quarter last year, and the company will get a further bump when it refreshes its MacBook line, an analyst said today. That refresh could come this week.

The Cupertino, Calif. company is on track to sell 3.6 million Macs, said Stephen Baker, analyst with the NPD Group, a company that monitors retail and online sales. Apple sold 2.9 million Macs in the first quarter of 2010.

Sales will pop in the next four to six weeks, added Baker, if Apple ships new MacBook Pros this week, as reports increasingly hint.

"Usually there is a significant bounce in the first month to six weeks and then a concurrent slowdown for a few weeks after that," said Baker, talking about Apple's sales trends when it refreshes a line. "Within two months the growth rate turns back to normal and the cumulative growth rate for the bounce and decline typically also results in a return to the trend line."

Another analyst cautioned that any bump Apple gets from new notebooks might be cumulatively smaller than Baker expects.

"What we don't know is how much of that bump is due to pent-up demand," said Ezra Gottheil of Technology Business Research. "Apple definitely gets a bump with refreshes, but some of that may be from customers who delayed purchases when they started hearing [about new models]."

According to numerous reports by Apple-centric blogs -- which have universally cited unnamed sources -- Apple will refresh its MacBook Pro line-up Thursday, turning to new Intel processors and chipsets, and adding an Intel device connection technology called Light Peak .

Baker sees Apple's penchant to space out new product announcements as more about public relations than about keeping sales steady throughout the year.

"They want each launch to get maximum attention and the best way to do that is to space them out," Baker said.

He also noted that, like other computer makers, Apple is tied to Intel's processor release cycles. "Despite their best efforts they still remain, to at least some extent, although not as much as the Windows guys, beholden to Intel's refresh cycle," Baker said.

By spacing out product announcements -- MacBook Pros this week, for instance, a new iPad likely soon after -- Apple also reduces pressure on its supply chain and retail stores, Baker added.

Apple's iMac desktop line is also nearing the time when it could be updated. The MacRumors Buying Guide , which tracks the intervals between Mac refreshes, currently notes that it's been 211 days since the last iMac revamp, close to the 226-day average.

"iMac sales have been much weaker than MacBooks and I think refreshes that keep that line relevant and current are more important to it than MacBooks, since the underlying demand for desktops is inherently weaker than the notebooks," said Baker.

In the last quarter for which Apple has released sales figures -- the fourth quarter of 2010 -- the company sold 1.2 million desktop systems, the bulk of them iMacs, compared to 2.9 million notebooks. Desktop sales that quarter were down 1% from the year prior, while notebook sales were up 37% over the same quarter in 2009.

Apple has foresworn public events for announcing most upgrades to its existing Mac lines, instead relying on press releases and new information on its e-store to carry the load. One recent exception to that rule was last October, when CEO Steve Jobs -- now out on an indefinite medical leave -- debuted the new MacBook Air by calling it "the future of notebooks."

Apple will also host its annual stockholder meeting today starting at 1 p.m. ET. It's not known if Jobs will appear, although he did attend a dinner last week with President Obama.